From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id AB8C57D90F for ; Thu, 14 Nov 2019 19:50:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726557AbfKNTus (ORCPT ); Thu, 14 Nov 2019 14:50:48 -0500 Received: from mail.kernel.org ([198.145.29.99]:35666 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726474AbfKNTus (ORCPT ); Thu, 14 Nov 2019 14:50:48 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [199.201.64.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C8BF420724; Thu, 14 Nov 2019 19:50:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573761046; bh=1ABanbOYD26kBQVaeu/qDUnt6KJkNmJdkzCHmVzodI0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=C2AGRCgtrKhkBetGWdjch+Z2IAWrzYfQtwzSHwSB5PbCo4q5pZvpBZXKWgF50aqUx 6Y5oHq06CBkAJs5x9D0Cd3hGqsP3+V1MLT/TNw57PZNDa5z1AFnkWyoJbOscWKyGBe kzO3uPGadX5naLrFF1gJZKemzgqia7+1a+hDPB/Y= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 7365535227FC; Thu, 14 Nov 2019 11:50:46 -0800 (PST) Date: Thu, 14 Nov 2019 11:50:46 -0800 From: "Paul E. McKenney" To: Marco Elver Cc: akiyks@gmail.com, stern@rowland.harvard.edu, glider@google.com, parri.andrea@gmail.com, andreyknvl@google.com, luto@kernel.org, ard.biesheuvel@linaro.org, arnd@arndb.de, boqun.feng@gmail.com, bp@alien8.de, dja@axtens.net, dlustig@nvidia.com, dave.hansen@linux.intel.com, dhowells@redhat.com, dvyukov@google.com, hpa@zytor.com, mingo@redhat.com, j.alglave@ucl.ac.uk, joel@joelfernandes.org, corbet@lwn.net, jpoimboe@redhat.com, luc.maranget@inria.fr, mark.rutland@arm.com, npiggin@gmail.com, peterz@infradead.org, tglx@linutronix.de, will@kernel.org, edumazet@google.com, kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-efi@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH v4 00/10] Add Kernel Concurrency Sanitizer (KCSAN) Message-ID: <20191114195046.GP2865@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191114180303.66955-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191114180303.66955-1-elver@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Thu, Nov 14, 2019 at 07:02:53PM +0100, Marco Elver wrote: > This is the patch-series for the Kernel Concurrency Sanitizer (KCSAN). > KCSAN is a sampling watchpoint-based *data race detector*. More details > are included in **Documentation/dev-tools/kcsan.rst**. This patch-series > only enables KCSAN for x86, but we expect adding support for other > architectures is relatively straightforward (we are aware of > experimental ARM64 and POWER support). > > To gather early feedback, we announced KCSAN back in September, and have > integrated the feedback where possible: > http://lkml.kernel.org/r/CANpmjNPJ_bHjfLZCAPV23AXFfiPiyXXqqu72n6TgWzb2Gnu1eA@mail.gmail.com > > The current list of known upstream fixes for data races found by KCSAN > can be found here: > https://github.com/google/ktsan/wiki/KCSAN#upstream-fixes-of-data-races-found-by-kcsan > > We want to point out and acknowledge the work surrounding the LKMM, > including several articles that motivate why data races are dangerous > [1, 2], justifying a data race detector such as KCSAN. > > [1] https://lwn.net/Articles/793253/ > [2] https://lwn.net/Articles/799218/ I queued this and ran a quick rcutorture on it, which completed successfully with quite a few reports. Thanx, Paul > Race conditions vs. data races > ------------------------------ > > Race conditions are logic bugs, where unexpected interleaving of racing > concurrent operations result in an erroneous state. > > Data races on the other hand are defined at the *memory model/language > level*. Many data races are also harmful race conditions, which a tool > like KCSAN reports! However, not all data races are race conditions and > vice-versa. KCSAN's intent is to report data races according to the > LKMM. A data race detector can only work at the memory model/language > level. > > Deeper analysis, to find high-level race conditions only, requires > conveying the intended kernel logic to a tool. This requires (1) the > developer writing a specification or model of their code, and then (2) > the tool verifying that the implementation matches. This has been done > for small bits of code using model checkers and other formal methods, > but does not scale to the level of what can be covered with a dynamic > analysis based data race detector such as KCSAN. > > For reasons outlined in [1, 2], data races can be much more subtle, but > can cause no less harm than high-level race conditions. > > Changelog > --------- > v4: > * Major changes: > - Optimizations resulting in performance improvement of 33% (on > microbenchmark). > - Deal with nested interrupts for atomic_next. > - Simplify report.c (removing double-locking as well), in preparation > for KCSAN_REPORT_VALUE_CHANGE_ONLY. > - Add patch to introduce "data_race(expr)" macro. > - Introduce KCSAN_REPORT_VALUE_CHANGE_ONLY option for further filtering of data > races: if a conflicting write was observed via a watchpoint, only report the > data race if a value change was observed as well. The option will be enabled > by default on syzbot. (rcu-functions will be excluded from this filter at > request of Paul McKenney.) Context: > http://lkml.kernel.org/r/CANpmjNOepvb6+zJmDePxj21n2rctM4Sp4rJ66x_J-L1UmNK54A@mail.gmail.com > > v3: http://lkml.kernel.org/r/20191104142745.14722-1-elver@google.com > * Major changes: > - Add microbenchmark. > - Add instruction watchpoint skip randomization. > - Refactor API and core runtime fast-path and slow-path. Compared to > the previous version, with a default config and benchmarked using the > added microbenchmark, this version is 3.8x faster. > - Make __tsan_unaligned __alias of generic accesses. > - Rename kcsan_{begin,end}_atomic -> > kcsan_{nestable,flat}_atomic_{begin,end} > - For filter list in debugfs.c use kmalloc+krealloc instead of > kvmalloc. > - Split Documentation into separate patch. > > v2: http://lkml.kernel.org/r/20191017141305.146193-1-elver@google.com > * Major changes: > - Replace kcsan_check_access(.., {true, false}) with > kcsan_check_{read,write}. > - Change atomic-instrumented.h to use __atomic_check_{read,write}. > - Use common struct kcsan_ctx in task_struct and for per-CPU interrupt > contexts. > > v1: http://lkml.kernel.org/r/20191016083959.186860-1-elver@google.com > > Marco Elver (10): > kcsan: Add Kernel Concurrency Sanitizer infrastructure > include/linux/compiler.h: Introduce data_race(expr) macro > kcsan: Add Documentation entry in dev-tools > objtool, kcsan: Add KCSAN runtime functions to whitelist > build, kcsan: Add KCSAN build exceptions > seqlock, kcsan: Add annotations for KCSAN > seqlock: Require WRITE_ONCE surrounding raw_seqcount_barrier > asm-generic, kcsan: Add KCSAN instrumentation for bitops > locking/atomics, kcsan: Add KCSAN instrumentation > x86, kcsan: Enable KCSAN for x86 > > Documentation/dev-tools/index.rst | 1 + > Documentation/dev-tools/kcsan.rst | 256 +++++++++ > MAINTAINERS | 11 + > Makefile | 3 +- > arch/x86/Kconfig | 1 + > arch/x86/boot/Makefile | 2 + > arch/x86/boot/compressed/Makefile | 2 + > arch/x86/entry/vdso/Makefile | 3 + > arch/x86/include/asm/bitops.h | 6 +- > arch/x86/kernel/Makefile | 4 + > arch/x86/kernel/cpu/Makefile | 3 + > arch/x86/lib/Makefile | 4 + > arch/x86/mm/Makefile | 4 + > arch/x86/purgatory/Makefile | 2 + > arch/x86/realmode/Makefile | 3 + > arch/x86/realmode/rm/Makefile | 3 + > drivers/firmware/efi/libstub/Makefile | 2 + > include/asm-generic/atomic-instrumented.h | 393 +++++++------- > include/asm-generic/bitops-instrumented.h | 18 + > include/linux/compiler-clang.h | 9 + > include/linux/compiler-gcc.h | 7 + > include/linux/compiler.h | 57 +- > include/linux/kcsan-checks.h | 97 ++++ > include/linux/kcsan.h | 115 ++++ > include/linux/sched.h | 4 + > include/linux/seqlock.h | 51 +- > init/init_task.c | 8 + > init/main.c | 2 + > kernel/Makefile | 6 + > kernel/kcsan/Makefile | 11 + > kernel/kcsan/atomic.h | 27 + > kernel/kcsan/core.c | 626 ++++++++++++++++++++++ > kernel/kcsan/debugfs.c | 275 ++++++++++ > kernel/kcsan/encoding.h | 94 ++++ > kernel/kcsan/kcsan.h | 108 ++++ > kernel/kcsan/report.c | 320 +++++++++++ > kernel/kcsan/test.c | 121 +++++ > kernel/sched/Makefile | 6 + > lib/Kconfig.debug | 2 + > lib/Kconfig.kcsan | 118 ++++ > lib/Makefile | 3 + > mm/Makefile | 8 + > scripts/Makefile.kcsan | 6 + > scripts/Makefile.lib | 10 + > scripts/atomic/gen-atomic-instrumented.sh | 17 +- > tools/objtool/check.c | 18 + > 46 files changed, 2641 insertions(+), 206 deletions(-) > create mode 100644 Documentation/dev-tools/kcsan.rst > create mode 100644 include/linux/kcsan-checks.h > create mode 100644 include/linux/kcsan.h > create mode 100644 kernel/kcsan/Makefile > create mode 100644 kernel/kcsan/atomic.h > create mode 100644 kernel/kcsan/core.c > create mode 100644 kernel/kcsan/debugfs.c > create mode 100644 kernel/kcsan/encoding.h > create mode 100644 kernel/kcsan/kcsan.h > create mode 100644 kernel/kcsan/report.c > create mode 100644 kernel/kcsan/test.c > create mode 100644 lib/Kconfig.kcsan > create mode 100644 scripts/Makefile.kcsan > > -- > 2.24.0.rc1.363.gb1bccd3e3d-goog >